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eldavojohn writes "There's a new antenna that consists of plasma and essentially vanishes when you turn it off. While it may seem to not have many uses in the commercial world, it is very important to military personnel who risk detection or for anybody wishing to avoid signal jamming."

Because it's a plasma antenna, it's tunable on the fly. No jamming tech ( though it will surely follow ) works on every f at once. The invisibility is just because it shuts off so then is basically inert.

Still, if you are transmitting voice on let's say 150 Mhz and someone is transmitting a high pitched whine (taking up more bandwidth, thusly...16khz or so) at a higher amplitude than your voice transmission, it's gonna get cruddy. Even FM gets F!'ed up by this. Then again, all you have to do is change frequencies, but I don't see where attenuation comes in handy for defeating a broadband jammer.Same principle would apply to airborne data transmission, I would think. Correct me if I'm wrong, I only renewe

I don't disagree with you - and I'm a "good" ham (whatever that means;-)I don't believe these claims - they're just stupid. Anti-jam? For instance - you want the antenna to disappear? If we're talking on a HUMMV - what the heck. Just turn the radio off???? That is how you disappear electronically.

As for the noise crud the plasma generator and the high voltage will make - maybe it can be filtered, but think of all the juice you're wasting creating the plasma field!!! A hunk of metal seems a more effici

They can, but only for short periods (which actually puts a low limit on the frequency of jamming ; could you jam a 1Hz carrier wave with a noise source that operates for 0.3 seconds? Since I spend a good part of my working day using signals transmitted over 1Hz links against 0.5~0.25Hz noise sources, I know it's going to be difficult). But the integrated power output from gamma rays to low-frequency radio waves is comparable to t

Well, in the words of my German air force buddy who is now a Patriot missile operator: "If I can't fly, nobody can."Probably something akin to that. Then again, a given handheld or even vehicle mounted radio only has SO much bandwidth upon which it can transmit...it's not quite as simple as simply changing frequency to avoid a jammer, as noted with the wiki link above. A base or a naval vessel has quite a bit more flexibility, and thusly broadband jamming would be harder (plus they can potentially overpow

There are lots of antennas that are tuneable on the fly. Diode switching can do that. So can mechanical antennas. At microwave frequencies, conventional antennas can be very broad-banded.Oh, and jamming actually DOES work on many frequencies at once. Ever heard of repeating jammers? Something else to consider: Jammers used against radar don't need to be as powerful as the radar. They only need to cover up the echo. The echo dies off according to the distance to the fourth power. The more powerful t

Antennas are not stealthy. They have a radar signature, but glass has a minimal radar signature. So the tube should not be as non-stealthy as attaching a chunk of metal to an otherwise stealthy piece of equipment.

Yes - and no:)The gas is hot, but at very low pressure. So the amount of energy transmitted to the glass container surrounding it is minimal, and could be further reduced by active cooling. So the second your incomings are detected and the antenna shuts down it becomes invisible to both the RF and infrared seeker.

I don't quite get the usefulness of this thing either - when it's turned on, there's bright glowing plasma, and when it's turned off, even though it doesn't have a long metal piece, it still has a lot of metallic support machinery, plus it's a glass tube that you need to haul around carefully instead of a metal antenna or rubber ducky that you can bang into things.

You can fabricate some pretty sturdy pieces of glass that you could beat a person to death with, It's going to cost you a fortune but thats hasn't stopepd the military yet. If I remember correctly glass in theory is stronger then steel it's just that during the cooling process many micro fractures form in it.

Strength and cost varies widely depending on the type of glass you use. Borosilicate is pretty cheap, and I've seen rods of that thrown against a brick wall without taking any visible damage (I didn't check it with a polariscope - a tool used to view internal stresses in glass). If you need something stronger you can use fused quartz, ruby, and I'm sure many more exotic forms.

As far as the micro fractures thing? That's not quite correct. What you get is a build up of internal stresses. This weakens the glass, and reduces it's ability to handle thermal and mechanical shocks. I may be mistaken, but I believe this is related to the coefficient of thermal expansion - basically as the outside of the glass cools it contracts. This leaves the cooled glass pushing against the pressure of the still molten glass, and once completely cooled, that stress remains.

That's all pretty much a non-issue though. Controlled cooling in an annealing oven takes care of it well enough.

Sorry to double post, but there are a few things I thought about after writing this...

First off, I mentioned a borosilicate rod thrown against a brick wall. Just for the sake of completeness, this was a 3/8" rod about 3" in length, flame polished on both ends and annealed.

Secondly, I mentioned ruby glass... That could lead to a misunderstanding. "Ruby glass" generally refers to a method of coloring a softer glass to give it a ruby like color - that's not what I'm talking about. I mean fused ruby, wh

It's been a while since my inorganic chem classes, but can't ruby be synthesized? I seem to recall that high quality is difficult to acheive, but if you're just going to melt it down, you only need fairly small bits to be somewhat uniform. It may not be as tough as natural ruby (don't remember) but it's still going to be damn strong.

yeah.. all ruby is, is aluminum oxide. in crystalline form. the created rubies / emeralds / sapphires are essentially identical to their natural counterparts in composition and structure these days..it can be synthed without too much trouble, but the cost of an alum.ox. antenna would still probably be pretty high, though. while it's cheaper to create a gem in the lab than buy a wild one, that's just for gem-sized pieces. it'll cost a fair shake regardless if you're talking about FEET (or METERS) rather

Yeah, the only differences are the impurities that give the colours right? But in terms of making crystals just to be crushed and melted down, this could likely be done a little cheaper cause they're not worried about making jewelry. And cost tends to be less of a factor when it comes to military applications, not completely unimportant, but certainly not the main issue. And how much of the cost of synthetic gems is the lab/company trying to make a profit as opposed to the raw materials/energy?

>Borosilicate is pretty cheap, and I've seen rods of that thrown against a brick wall without taking any visible damage

Go you one better: Prince Rupert's Drops [wikipedia.org]. Drip molten glass into water. The few that survive are incredibly, unbelievably tough -- I've made ones the size of peas (well, teardrop-shaped peas) and put them on a vise and hammered them with a steel hammer and left dents in the vise back and the hammer face, without hurting the glass. When that gets boring, you snap the long tail that was

Been a while since I checked replies, but just let me say, thank you! I was struggling to remember the name of those things when I first posted... That was one of the things presented to me on one of my first days in a glass shop - somewhere between flame polishing, pulling points, puntys, and "mushroom beads".

I first found out about them by accident. Had a mason jar full of water at my bench that was mainly used to quench and break off glass that I didn't need. Had a drop form on accident, and the gu

One very simple way to counteract jamming is to note that the jammer is not omnipresent. That is, the jamming source is often only present in a small radian-angle of the antenna's radiation sphere. Therefore, you can counteract jamming by configuring your antenna to place a null in the direction of the jammer (i.e. ignore the annoying little kid) and radiating elsewhere. Alternatively, if you know where you want to either transmit a signal or receive a signal, you can create a beam to point in that direction by reconfiguring your antenna. In both cases, it is usually standard practice to use an array of antennas.
This invention (and no, it's not really a new idea, but perhaps the engineering makes it more reliable or easier to manufacture than in the past) allows you to place a large antenna array on an aircraft without permanently increasing the RCS of said aircraft, since the antennas only exist when you charge up the plasma. A large antenna array can create a narrow beam and place several nulls using conventional technology. All of this stuff exists today, so these plasma antennas just need to replace metal antennas and away you go. The really interesting application of these antennas could actually be to create 3D reconfigurable antennas using DC-magnetic fields (kind of like a CRT, but with more magnets).

This is an old idea. Look in Kraus, Antennas, Third edition. Section 21-29. Also see patent 6657594.
The point is the RCS of the antenna is lower when the plasma is off, they efficiency of this type of antenna isn't that high.

How does having the antenna "disappear" effect it's ability to circumvent jamming?

I'm a bit foggy how it "disappears". Last I checked, you need some type of container to shape plasma into a cylinder, so while the plasma may disappear, the giant glass tube presumably will still be there...and why does the author keep calling plasma a gas? Yes, you get plasma by superheating a gas. You get gas by heating liquid. Doesn't make gas the same as liquid. Plasma isn't the same as gas either.

The glass tube doesn't dissapear. Think of a fluorescent tube: when it is lit, it radiates light and non-visible EMR, but when it's off, it doesn't. Now ideally, a metallic antenna won't either, but since it's a conductive material, nearby electric and magentic fields will induce magnetic and electric fields which *could* be detected or, more practically, a metallic antenna will reflect EM waves that strike it whereas glass won't (or at least will do so to a far lesser extent).
A far more realistic problem

How does having the antenna "disappear" effect it's ability to circumvent jamming?

A metal antenna can be detected just like any other large metal object. When you kill the juice to this, it just disappears, so you don't have any large metal bits to stow.

What gets me is how the plasma isn't a signal emitter in its own right. I mean, we are talking electric arc discharge, like an neon sign, like a spark gap, like lightning. I had always thought an electric arc was a broadband RF transmission. That should be detectable in every direction.

When I submitted this story, I submitted the story from PhysOrg [physorg.com] and I'm not sure why they changed the link. That poor blog didn't stand a chance. I guess they must do that to more randomly distribute their news sources or make it look like they aren't playing host to some PhysOrg worker trying to generate more traffic. Oh well, enjoy a usable link anyhow.

Greetings,
It doesn't really prevent jamming, though it does give them a variable antenna, by tuning the plasma, thereby improving their ability rapidly change radio frequencies etc. This give them the ability to reduce the affects of single band jamming and even some multi-band jamming. It actually seems pretty clever, though, I really fail to see it's battlefield value as there will be a tremendous amount of heat given off by the plasma field. Now shipboard and some amored cav use

You can view it as an electrically switchable conductor. Turn the power on and you have a conductor. Turn it off and you get an insulator. The problem is that it takes power to maintain. As long as you have adequate power, you can make a conductor. If you have lots of power, you can ionize atmospheric pressure air, but we do mean lots of power. At low pressure, you need less power, but you have the corresponding issue of fragility of the supporting structure, which must be both strong and insulating.

I assume that the technology would be more useful in radar sources, where you could do a short term illumination of a target and then turn it off. A sensor trying to pick up the antenna when it was not powered might well have a significantly harder time than with a traditional antenna.

The original link works for me'Stealth' Antenna Made Of Gas, Impervious To JammingSubmitted by News Account on 12 November 2007 - 2:58pm.Physics

A new antenna made of plasma (a gas heated to the point that the electrons are ripped free of atoms and molecules) works just like conventional metal antennas, except that it vanishes when you turn it off.

That's important on the battlefield and in other applications where antennas need to be kept out of sight. In addition, unlike metal antennas, the electrical chara

'Stealth' Antenna Made Of Gas, Impervious To Jamming
Submitted by News Account on 12 November 2007 - 2:58pm. Physics

A new antenna made of plasma (a gas heated to the point that the electrons are ripped free of atoms and molecules) works just like conventional metal antennas, except that it vanishes when you turn it off.

That's important on the battlefield and in other applications where antennas need to be kept out of sight. In addition, unlike metal antennas, the electrical characteristics of a plasma antenna can be rapidly adjusted to counteract signal jamming attempts.

Plasma antennas behave much like solid metal antennas because electrons flow freely in the hot gas, just as they do in metal conductors. But plasmas only exist when the gasses they're made of are very hot. The moment the energy source heating a plasma antenna is shut off, the plasma turns back into a plain old (non conductive) gas. As far as radio signals and antenna detectors go, the antenna effectively disappears when the plasma cools down.

The antenna design being presented at next week's APS Division of Plasma Physics meeting in Orlando consists of gas-filled tubes reminiscent of neon bulbs. The physicists presenting the design propose that an array of many small plasma elements could lead to a highly versatile antenna that could be reconfigured simply by turning on or off various elements.

So what's you're saying is that this conversation is no longer fiction:

Radio Operator: Sir! I can't get through to base!Officer: damn, they must be jamming our transmissions! Try inverting the phase polarity!Radio Operator: That did it! I have communications.. here..Officer: General, the enemy is capable.

These antennas sound interesting, reconfigurable and all that, but I am guessing that their noise performance must be awful. And I mean electrical noise not audio noise for those out there who are confused. Usually in an RF system you want as little noise up front as possible, and noise goes up with temperature. So this is an antenna made of very hot plasma as the very first element in the receiver system.

I keep thinking that the accelerated gas atoms are going to sputter the electrodes. The last thing I'd want in an antenna is having to carry around a gas cylinder just to maintain the operating pressure. Because as whatever gas is used, the atoms are going to embed themselves into the electrode lowering the pressure. This maybe less of an issue if they drive it with an AC source rather than DC, but it's certainly something to consider. Awesome that someone is doing this though, I was thinking about this

In a normal antenna, electrons in the metal slosh up and down, accelerated by the electromagnetic fields that it's receiving (or transmitting). In this case, I could use the same description: electrons slosh up and down, driven by the EM fields.

The idea that this could lead to a reconfigurable antenna is a bit farfetched, as it would require that the driving bias electrodes be able to totally float at RF frequencies. Just like a neon sign, or a fluorescent light, you're going to have to keep a large voltage across these to get them to light, so it'll be tricky to use it as a receiving antenna in particular.

Take a look at another project, Talking Lights [talking-lights.com]. This uses conventional fluorescent lights (hey, a plasma!) with a modified ballast to transmit data at serial-link speeds.

The "jam-resistance" doesn't make any sense. If it can receive signals, it can receive signals, period. At the point of the antenna, the desired signal and the jamming signal have already been mixed. The antenna itself can't help you out. (Clever frequency-hopping or other schemes can, though.)

Install a listening device in an embassy meeting room. Records many weeks of conversations. Does not broadcast. Also has a radio receiver.

Prior to an electrical storm, drop a package on the roof using a rapid-descent parachute. It looks like a chimney or AC unit, with a large pole on top that functions as a lightening rod. The box sends a signal to the inside recorder that tells it to broadcast a burst of encrypted data to the box then when lightening hits the pole, it becomes a plasma attenna that can broadcast the data over a long distance. Oh, and the electricity from the lightening powers the whole operation. Then the box self-destructs on the roof.

Back in my university days I had the pleasure of being taught by a physicist turned engineer who was actually working on one of these things. The trouble with traditional antennas is their giant radar footprint and traditionally they solved this problem by flopping the antennas up and down when they needed to send signals. Not the most graceful solution so they started looking for alternatives.
We had one of the prototypes of these things in the plasma instrumentation lab and it was pretty adept at sending some small signals. The great thing about them is their tunability. Just like any kind of woodwind instrument if you change the length of the tube (imagine a giant piston that's got plasma in it) you change the resonant frequency. My lecturer referred to it as playing the plasma trombone.
Good to see these things finally making their way through to practical uses. I was always hoping my crazy lecturer's tinkerings would be used someday.

Minor musical nitpick: (modern) brass instruments, such as the trombone, change resonant frequencies through changing the length of the tube. Woodwind instruments change effective lengths in ways that probably don't work so well in describing antennas.

The pic from TFA looks a bit dainty for combat use. I think a whip antenna is probably still more reliable and has a smaller radar signature for short range communication (IE a couple dozen miles). And the big ones, well, there's no hiding them.

Plus that whole bright and hot thing tends to attract the attention of certain guided missiles and sensor systems...not good! Maybe if they paint the glass or something...at least the light problem is solved.

You only think its hot because it's glowing and the description has the word plasma. In truth, because of the low density of gas, I doubt the actual heat energy dissipated is much more than a fluorescent bulb. If the enemy is close enough to see the antenna on IR, they're close enough to see you.

I reposted the article just above. The picture shows a glowing u-shaped florecent tube. By "disappear" I believe they just mean large radar return. Such materials are called PECs in radar parlance (Perfect Electrical Conductor). You will still be able to see the tube visually.

In related speculation, I wonder if you could use the ION beam from a space probe's thruster (assuming Ion Drive of course) as an antenna. Of course since it wouldn't be parabolic or very directional it might be of limited use.

If it needs glass tubes to work, its not like it will just 'dissapear', and would be a lot more fragile than a metal one. That might be ok for light use, but stick it out in the battlefield and i dont see it holding up for long.

Might work disguised as a neon 'eat at joes' lamp for undercover work..

It also mentions needing several 'segments' to prevent jamming. Couldn't this also be done with more traditional antennas?

This might have a small physical cross-section on radar, but I'm not sure that's enough to compensate for the plasma......I work in an electronics lab, and occasionally we use a sputtering system - which generates a ball of plasma to transfer ions from one surface to another. Anyway, point being, when we do this, the guys next door, who do a lot of RF measurements, go absolutely nuts - because we've just screwed all of their instruments and currently-running measurements. (Incidently, between them and th

I work in an electronics lab, and occasionally we use a sputtering system - which generates a ball of plasma to transfer ions from one surface to another. Anyway, point being, when we do this, the guys next door, who do a lot of RF measurements, go absolutely nuts

Have you completed RF leakage testing? Is the RF screen in place in the quartz windows? Is the cable secure between the RF gen and the matching network? Is the RF gasket in place between the match and the chamber. There is no reason to have e

That would be the Apple iPlasma phone. Not only can you make calls, listen to music, and watch videos on it, but you can extend the plasma antenna and kill people who are using ordinary cell phones. Especially the annoyingly talkative oblivious ones in restaurants, movies, or grocery lines.

The iPlasma -- flaming death in a compact shape -- only from Apple. Note: We only accept cash, and only two iPlasmas to a customer, please.

antenna that consists of plasma and essentially vanishes when you turn it off. While it may seem to not have many uses in the commercial world,

Everyone who parks their car in NYC and other hostile environments wants an antenna that vanishes when you turn it off. Plasma probably wouldn't jam after a year of use like a retractable antenna, and might even clean the snow off your car, including the pile burying you from the street plows.

Well, the "stealth" antenna in the article is a huge, glowing tube. According to the article, the antenna is indeed made of "gas-filled tubes reminiscent of neon bulbs."I wouldn't call an neon sign "essentially vanishes" when it's turned off.

There's no indication in the article that they can generate the plasma without a confining tube, but even if they could, like the Cheshire cat's grin without the cat, it would still be pretty conspicuous when it's on.

Metallic antennas are excited by EM radiation (radio waves) of a proper wavelength. In turn, the antenna will re-radiate (transmit) a tiny bit of that energy, although very weakly, which can be detected. This is totally passive, which is how it is possible to build a passive repeater by simply running a wire between two directional antennas. It is also the general principal of how RFID tags work.

The stealth of this antenna is that it is non-metallic and will not react to EMF when switched off. It has nothing to do with how big the antenna is, or what color it is, or whether or not it emits light, which are all things people have been speculating about.

So, it 'vanishes' when it is off? When it is on it lights up like a neon sign? I could be wrong - but a gigantic neon light antenna up in the air is going to be a pretty obvious target. The enemy is going to know exactly where you are. Also - they are going to know you are transmitting something - so they can start to jam/home in on your signal. How exactly does this prevent that?Also - I would love it if the enemy used this brilliant antenna design. You will be left flabber"gas"ted as I use my ultra-portab

I remember seeing this stuff more than 10 years ago. Being Australian the stuff I saw ten years ago was from an Australian University grant from the DSTO (military research organisation), with information that can be found at http://wwwrsphysse.anu.edu.au/~ggb112/ [anu.edu.au]

In fact a Typical Fluroscent tube makes a reasonable HF antenna with its frequency dependent on its length. For those that think the glowing plasma makes the antenna detectable in the visible spectrum, its easy to have a material that is opaque in

Disguise it as a stealth-plasma flagpole and proudly fly a red-white-and-blue flaming sheet-o-plasma flag! Has the added advantage of shocking the hell out of any pot-smoking hippies who try to burn it!

The real application for this might be in space. It's very hard to hide your satellite from the incoming kill vehicle if you have a huge antenna deployed. This technique could actually project a "ghost antenna" just off the satellite, and since this is not horse shoes, close does not count.

Furthermore, the noise this thing produces will stand out like a sore thumb for a HARM (High speed Anti Radiation Missle) missle.

There is no reason it needs to be any noisier than a F40 florescent tube. Last time I checked, neon signs and florescent lights didn't attract HARM missiles. These tubes can be sensitive to HF and VHF while excited by DC or low frequency square wave AC. HARM missles due to the limited size of the RF direction finding is mostly limited to Microwave and UHF. HARM missiles mostly

a vacuum also conducts electricity.Maybe not as well.could they use a vacuum?

Only when there is a source of free electrons nearby. A CRT works by having an electron gun in the back. When it is dead, the electron flow stops. Add a small amount of gas and excite it and you have a low pressure plasma much like in a neon tube or plasma sphere. A vacuum is used as an insulator. Here is an example..